1. Field of the Invention
The present invention relates to a control apparatus for a dual clutch transmission, i.e., a transmission including a plurality of clutches, and to a control method for the dual clutch transmission.
2. Description of the Related Art
A conventional dual clutch transmission, which is mounted on a motor vehicle and includes a plurality of clutches for fast gear changes of the motor vehicle, (referred to simply as “transmission” below in some case) and a control apparatus to control the dual clutch transmission are known (see, for example, Japanese Patent Application Laid-Open No. 2004-251456 and Japanese Patent Application Laid-Open No. 2004-308841).
The transmission includes a plurality of clutches disposed between an engine and input shafts of two systems, each clutch being capable of transmitting a driving force or blocking the transmission of the driving force, and pairs of gears divided into the two systems (e.g., two systems of an odd transmission stage group and an even transmission stage group) that selectively connect the input shafts of the two systems and a transmission output shaft (hereinafter referred to simply as “output shaft”) according to a shifter selection.
In this transmission, while power is being transmitted to one of the pairs of gears in one transmission stage group that is connected to one of the clutches by engaging the one clutch and is selected by the shifter, the pairs of gears in the other transmission stage group corresponding to the other clutch can be kept in a neutral state, where no power is transmitted, by selecting through the shifter while the other clutch is held in engagement. That is, in a state where the two clutches are engaged, power can be transmitted from the output shaft to a drive wheel through the desired pair of gears in the transmission stage selected by the shifter.
Also, at the time of changing gears, the other clutch of the plurality of clutches associated with the transmission system of the transmission stage group not transmitting power is released. One of the pairs of gears in the transmission system including the input shaft connected to the other clutch is then selected and shifted into the target transmission stage. The other clutch is thereafter engaged while the one clutch that has been transmitting power is released.
That is, in the conventional dual clutch transmission, when a transmission stage is shifted from a selected and operational transmission stage (also referred to as “previous stage”) to a target transmission stage (also referred to as “next stage”), a control apparatus performs interchanging of the clutches by simultaneously operating the clutches, i.e., by releasing the clutch that is transmitting power and by engaging the clutch that is to transmit power through the following transmission stage (next stage) in a state where the pairs of gears in the two transmission systems are connected.
As described in Japanese Patent Application Laid-Open No. 2004-251456 and Japanese Patent Application Laid-Open No. 2004-308841, when controlling the conventional dual clutch transmission in which interchange between the plurality of clutches is performed while the clutches are being operated simultaneously, it is necessary to keep the sum of the torque capacities of the clutches simultaneously operated equal to a target value such as a value of the engine torque on a clutch portion from beginning to end of the clutch interchange in order to avoid shift shocks (including a change in vehicle speed, and pitching) caused by the interchange as effectively as possible.
In the following description, a clutch that is being used and that is to be interchanged is referred to as a “release-side clutch”, and a clutch that transmits a torque in engagement after gear change is referred to as an “engaging-side clutch”.
According to the transmission control of a conventional dual clutch transmission that is mounted on a motor vehicle or the like, in a torque transmission path change phase, clutch interchange is performed by simultaneously operating a plurality of clutches including both a release-side clutch and an engaging-side clutch.
When performing clutch interchange control that is used in a motorcycle, if a malfunction occurs in the engaging-side clutch, in the case of a power-on upshift state, since both clutches are disconnected, the engine rotational speed increases excessively and a shift shock is caused.
In this case, the following situation is assumed with respect to a malfunction of the engaging-side clutch. In the clutches, there is a possibility of occurrence of immobility such that the clutch does not move from the current state. Immobility is sometimes called “clutch sticking” (referred to as “sticking” below). The term sticking refers to immobility from the current state rather than adherence of a clutch. For example, the state of the clutch does not change from a state of being held out of engagement, the clutch remains out of engagement, and from a state of being held in engagement, the clutch remains engaged. Although there is a possibility of the sticking occurring in each of the release-side clutch and the engaging-side clutch, a problem arises in the clutch interchange control when the sticking occurs in the engaging-side clutch. That is, in the torque transmission path change phase, when in a power-on upshift state, if the engaging-side clutch does not engage, since the load is disconnected, the engine rotational speed increases excessively. Since the torque is disconnected, an attempt is then made to engage the clutch, and inertial torque is produced and a shift shock is caused. If sticking occurs in the release-side clutch, double engagement is caused by the BTL (back torque limiter), so that braking is effected and a particularly large clutch malfunction does not occur.
A malfunction (sticking) in the engaging-side clutch is difficult to predict until clutch interchange is actually performed. Furthermore, since a certain time period (for example, 50 ms) is required to determine the sticking, the occurrence of an excessive increase in the engine rotational speed cannot be suppressed or prevented. Note that an excessive increase in the engine rotational speed due to sticking that occurs in the engaging-side clutch in this manner is not liable to occur in a motor vehicle because the rotating mass of an engine thereof is greater than in a motorcycle and the weight is also greater than in a motorcycle.